Long-term Borrowings - Components of Long-term Borrowings (Parenthetical) (Detail)			12 Months Ended
Jan. 17, 2017	Jul. 18, 2013	Dec. 31, 2017	Dec. 31, 2016
5.0% Exchangeable Senior Notes due March 2021 [Member] \| Exchangeable Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	5.00%		5.00%
Due date	Mar. 01, 2021		Mar. 01, 2021
6.625% Senior Notes Due 2021 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate		6.625%	6.625%	6.625%
Due date		Jul. 15, 2021	Jul. 15, 2021	Jul. 15, 2021

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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